Pressure variations of the 5f magnetism in UH3

Abstract

Pressure variations of the Curie temperature of the 5f ferromagnet beta-UH3 were studied using the Mo-alloyed hydride (UH3)(0.)Mo-82(0).18, which is stable in air and has very similar T-C and magnetization per U atom. By means of ac magnetic susceptibility a linear decrease of T-C was observed for pressures up to 3.2 GPa. The coefficient dT(C)/dp = -2.05 K/GPa gives dlnT(C)/dp = 1/T*dT(C)/dp approximate to -0.011 GPa(-1). This value is smaller than expected for a 5f-band ferromagnet with relatively short U-U distances and suggests that UH3 may be more localized than expected. Among AnX compounds, similar dependence was found e.g. for US. Revisiting existing data on lattice elasticity for beta-UH3, bulk modulus B approximate to 100 GPa can be assumed, leading to dlnT(C)/dlnV = 1.1. Experimental data are confronted with results of GGA + U electronic structure calculations. Plausible values of direct Coulomb U and Hund's exchange J are deduced. The lattice compression was found to reduce predominantly the orbital moments.